Starship Century, Part Two

by Paul Gilster on June 16, 2013

Adam Crowl concludes his discussion of the recent Starship Century conference in San Diego. Videos from the session are now becoming available online.

by Adam Crowl

Lunch at the Starship Century Symposium was provided by UCSD, allowing attendees to remain nearby, adding to the discussion and trading of ideas and concerns. Certainly I appreciated the chance to catch up with friends and faces from the other side of the Pacific, as well as meeting new people. Having read people’s novels, books or scientific papers for years, then meeting them on Facebook or email, I felt like I knew some of them already. Meeting authors that I had grown up with like Larry Niven, Joe Haldeman or David Brin was something I was getting used to, as I was more eager to discuss their interstellar ideas than succumb to fan-shock. I finally had my ideas about Larry Niven’s fusion-shield, from his “Known Space” stories, confirmed by the source, but didn’t quite get to talk to David Brin about the Fermi Paradox during the whole event.

The afternoon of the first day was thematically about “New Space” – what we’re doing, as a species, in the near term of a commercial nature. Of course, this was largely from the North American perspective. Patti Grace Smith [video], one of the senior Regulators of “New Space” in Washington DC, spoke about her role in helping commercial space efforts by creating a more operator friendly legal environment. Patti also gave a summary of the key-players in commercial sub-orbital and orbital commercial space efforts, the most prominent being SpaceX, while the most secretive has been Blue Origin, whom Patti has encouraged to be more open.

Image: Patti Grace Smith speaks on commercial space.

Beyond Chemical Propulsion

Once we’re in orbit the only way is Out – into the wider Solar System. Chemical propulsion isn’t up to the task, so Geoffrey Landis [video] made the argument that Nuclear Thermal Rockets (NTRs) will be the “Workhorse of the Solar System”. Geoff’s presentation was based on material presented previously, to more technical audiences, and the technical reports he referenced are also widely available. So he focussed initially on the long history of the NTR in astronautics – dating back to the late 1940s and almost brought to operational readiness by NASA’s nuclear rocket program, before being shelved in the early 1970s. Since then research has focussed on newer materials and newer testing techniques of reactor designs, largely via computer simulation and hot hydrogen gas experiments to simulate the operating environment of engine components. An important point is that NTRs allow transport of humans and their machines in reasonable time-frames all the way to Jupiter. Inside the orbit of Jupiter there exist many sources of the chief NTR propellant – hydrogen – usually in solid form attached to oxygen as water. Conveniently water has many other uses for human beings, thus will be in demand.

Image: Ian Crawford (left) and Geoffrey Landis.

That key point lead neatly into the next presenter’s talk. Chris Lewicki [video] of Planetary Resources gave an intriguing overview of the next steps for one of the first “asteroid mining” companies. Chris had clearly covered the material many times before, showing a polish that only comes with practice. The inner Solar System has abundant energy from the Sun, and convenient chunks of material orbiting in free space in the form of asteroids (and dead comets), but the first task is prospecting and finding the most convenient resources to retrieve from their distant orbits. Thus the Planetary Resources plan of building small satellites with autonomous control, to minimise ground-control costs, and many of them, to achieve savings via mass-production. Interplanetary prospectors that are cheap enough to crash into an asteroid if that’s what the mission requires. Eventually the quest for precious high-value materials in space to return to Earth will also have the side-benefit of producing great volumes of useful in-space materials, such as water. In time the inner Solar System could have a viable network of resource trading, with precious metals being dropped back to Earth via “whiffle-balls” of foamed metal, and storage depots of liquid hydrogen for Landis-style NTRs carrying people to the Moon, Mars and the asteroids.

With those thoughts in mind the day ended with a special presentation and viewing of a small fraction of Arthur C Clarke’s paintings and memorabilia, now at the Geisel Library. Seeing promotional material from 2001: A Space Odyssey”, signed by the actors, and similar items made me mindful of the vast legacy that Clarke’s work had inspired. In the nearly 50 years since he began working with Stanley Kubrick on 2001, we have achieved but a tiny part of what the 1960s imagined possible, a reminder of the difficulty of making dreams real.

Among the Starship Designers

Intense conversations ate up the hours after the scheduled activities, shadowed by my awareness that I was to be the first speaker on Day Two. My sleep was a broken few hours, an hour at a time, looking at the clock, while my subconscious was working on arranging what I would say. Needless to say, I have no idea how the delivery looked, as I covered slide-after-slide of starship concepts – most of which are covered in the anthology [video]. One gratifying aspect was being able to point out several starship designers in the audience – Freeman Dyson nodded approvingly when I discussed his interstellar Orion from 1968, and I discussed Al Jackson’s role in the development of the laser-powered ramjet. As a parting note I mentioned the “Ultimate Starship” – my personal suggestion, based on the late Robert Forward’s idea of a neutrino-rocket, to use electroweak unification physics to convert ram-scooped mass directly into a neutrino-jet. One day I will need to write the paper.

Jim Benford [video] covered the concept of microwave sail-ships, giving a fascinating look into his experimental work in the late 1990s with carbon-sails in vacuum chambers, being made to do amazing things via concentrated beams of microwaves. Jim, like his brother Greg, is a physicist, an alumnus of UCSD, but an applied physicist who has literally written the book on high-power microwave systems, such as the million-watt RADAR regularly used by the world’s armed forces. Thus he is well able to discuss the practicalities of propelling sails to interstellar speeds via beams of microwaves and has written several papers covering the economics of micro-wave starships. An elementary conclusion of the Benfords’ experiment is that a conical sail can very effectively ride a polarised microwave beam and be spun so it is self-stabilising. A less encouraging finding is that the cost of energy will dominate interstellar missions at high-speeds. Before we can reach the stars we will need to create abundant energy supplies.

Image: James Benford (left), Larry Niven and Gregory Benford at the book signing.

Next up was John Cramer [video], a physicist from the University of Washington, well-known to SF fans via his “Alternate View” columns in Analog, as well as several novels. John focussed on the use of wormholes to allow rapid transit to other star systems. Wormholes are simply connections between two points in space-time, compatible with Einstein’s equations of General Relativity as one possible mathematical solution. Outside the wormhole itself, observers would see two “ends” of the one space-time structure. Whether they exist or not is a matter for astronomical observation, as larger wormholes should produce distinctive gravitational lensing patterns that astronomers might be lucky enough to see.

If the connection formed between the two ends of a wormhole is shorter than the distance through regular space-time, then passing through the wormhole allows apparently faster-than-light travel, though nothing ever exceeds lightspeed locally. Thanks to time-dilation – the slowing of time experienced when approaching lightspeed – a time-lag can be developed between the two ends if one end is sent to a distant star. For example, if one end is accelerated to a time-dilation of 7,000 (0.99999999c), then only 75 minutes is required for the travelling end to appear to travel 1 light-year from the stationary end’s point-of-view. John Cramer discussed how this might allow a network of rapid-transit wormholes to be set-up throughout the Galaxy – with the caveat that the network can’t be allowed to form a “Closed Time-like Circuit” else this might destroy the wormholes via amplifying quantum fields.

On Target Stars and Life

Before lunch British astronomer Ian Crawford [video], a fellow member of Project Icarus, discussed what we might find amongst the nearer stars, out to 15 light-years. A planetary system probably exists around every star, something we can say with statistical confidence thanks to the work of the “Kepler” exoplanet detection mission, but discerning every planetary system will require improvements on current techniques. And we almost certainly haven’t found every small star within 15 light-years yet, as the 2013 discovery of a brown-dwarf binary at just 6.5 light-years should remind us. Ian made the forceful point that even with vast telescopes able to image those many new planets and stars, there’s only so much we can learn via telescopes. If we find a planet showing all the signs of life, we will only know more by actually going there – via robotic proxy, in Ian’s opinion.

Once we do go, will we survive? This was the after-lunch opener from Paul Davies [video], who posed the puzzling question of how terrestrial life might interact with truly alien life in another star-system. Could they co-exist, with no biochemical compatibility at all? Could they share common simple biochemicals, but foreign genetic and protein chemistry? Or could the two integrate in ways we haven’t yet imagined? Even more intriguingly, Davies suggested that we might already co-exist with “alien” biochemistries on Earth – organisms might exist in niches that otherwise exclude our kind of biology. A suggested location might be at temperatures higher than what known microbes can tolerate, or in highly alkaline fluids, such as what seeps from the ocean thermal vents. Davies has suggested, in more than one book, that any life on Mars shares a common ecosystem with Earth, due to the trade in meteorites between the planets over the aeons. Mentioning this sharing of life between planets produced an outburst from Robert Zubrin, who is an advocate of interstellar transfer of life throughout the Galaxy. A credit to Davies, his response was more interested curiosity than the reflexive dismissal Zubrin seemed to expect. His answer was that we simply don’t know enough to rule out the possibility and they should discuss it more later.

The Benfords encouraged researchers to present in the audience, with divergent points-of-view. These share a desire to bridge the space between the stars, but differ in details of how and why we’ll go to the stars. The next speaker unified the many voices by sharing his sense of wonder at the Universe, through a living work of art – Jon Lomberg [video] and his Galaxy Garden. Long-time readers of Centauri Dreams will know of Jon Lomberg’s artwork for Carl Sagan’s Cosmos in the 1970s and his Galaxy Garden in Hawaii. Having Jon share it with us, a guided-tour in slides, was inspiring and drew multiple rounds of applause from the audience. As Jon put it we can be Citizens of the Galaxy now.

Image: Artist and Galaxy Gardener Jon Lomberg.

Two discussion panels concluded the Symposium. The first, chaired by Jill Tarter, of the SETI Institute, featured Ian Crawford, Robert Zubrin, Geoffrey Landis, Paul Davies and myself. Our theme was “Getting to the Target Stars” but with Jill as the chair we wandered into the search for others who might have made the same journey [video]. Jill gave a brief summary of false-positive detections of extraterrestrial technology, which have proven to have natural explanations.

Image: Jill Tarter gives the lowdown on false-positives in SETI.

The sole exception, the distinctive spectroscopic signature of tritium, has no natural explanation if it is ever detected. With that in mind each of the panelists made suggestions about how we might detect aliens – Robert Zubrin mentioned the distinctive radio output of a starship deploying a magnetic sail, while I suggested the Solar System be searched for dead starships, since not everyone succeeds in their long voyages. A final task was to sum up how we thought humanity would go to the stars. A common feeling seemed to be via robotic proxies, or nanobots. In my opinion, by the time we are ready, the distinction between “human” and “robotic” might be meaningless or arbitrary – thus my quip “Nanobots are people too.”

The final panel [video] was a perspective by the science fiction writers, some involved in the Starship Century anthology – Joe Haldeman, David Brin, Larry Niven, Vernor Vinge – and Jon Lomberg. This was the artistic side of the event, as all these have produced visions of the starship era. The general feeling was that, given the growth in space industry that Chris Lewicki and Robert Zubrin advocated, then we would see the first star-voyagers depart in about 2200, much as Freeman Dyson had extrapolated back in the late 1960s. Some envisioned the unexpected – the discovery of extraterrestrial intelligence near enough to communicate with; breakthroughs in physics that would allow rapid interstellar travel; or, as Allen Steele depicted in his award-winning Coyote series, the rise of a tyrant putting a nation or the world on a crash-course program of starship-building. As always, the future will surprise us, but we can prepare ourselves by listening carefully to the modern-day prophets.

In the years 1865 and 1901 Jules Verne and H.G.Wells published their now famous novels “From the Earth to the Moon” and “The First Men in the Moon” respectively. Their ideas were not completely crazy, although the physics needed some work. In Verne’s novel the crew would be propelled to the Moon using a projectile mechanism, the same way a bullet is fired from a gun. That the acceleration would have killed the crew is a minor detail. In Wells’ novel, he decided to embark on what today we call a breakthrough propulsion physics device, painting the vehicle with a special kind of paint called Cavorite, which had the unusual property of effecting anti-gravitational lift.

We got to the Moon eventually, but the Saturn V was not quite the way these authors imagined it. At some point the ideas went from imagination to reality, as the examination of the physics and engineering technical issues became more credible. A technological transition occurred when the real lunar ship emerged into our world, and crystallised from a thing of thought, to a thing of matter and energy. Today, we imagine what a future starship may look like. And we are fortunate to live in an age where the idea is crystallising out of the imagination as many credible methods for how we accomplish this seemingly impossible mission begin to materialise.

Essentially, we are constrained by the ideal rocket equation, which expresses the additive velocity increments from successive engine stages, as a function of the vehicle exhaust velocity and mass ratio – the mass ratio being the ratio of initial wet mass (fuel + structure) divided by final mass (payload + structure) which arrives at the target. The objective is to get a high mass ratio, which means that the amount of mass remaining at the end of the mission should be a low percentage of the total start mass, although there is a trade-off because you want your payload fraction to be a minimum size.

Alternatively, one can have a high exhaust velocity, but this means choosing fuels which are energetic and release large amounts of energy/gram of substance. Typically, these go along the lines of chemical, nuclear fission, nuclear fusion, and antimatter. All starship designs which carry propellant rely on the ideal rocket equation in this way.

Some people like to search for “loop-holes” to this equation however, in the form of propellantless solutions. This includes using solar energy or stay-at-home laser propulsion, so that only the payload itself is accelerated. These are known as solar sail and laser sail type systems. You can combine rocket and non-rocket solutions in the form of the Bussard interstellar ramjet, which utilizes the interstellar hydrogen of space, funnelled in through a large magnetic scoop, as it accelerates up to the speed of light. Another hybrid is the Medusa sail, which combines elements of Orion nuclear pulse propulsion with solar sail technology.

When you look at starship design this way, through the lens of the ideal rocket equation, it’s almost as if nature has given us a toy to play with: “Here! Take this rocket equation, study it, bend it, exploit, it, perturb it, break it… find a way”. The stars call us ever closer by their glistening shines of light across the cosmos, beckoning us ever closer to discover the riches that orbit them on their myriad of worlds. But meanwhile, the ideal rocket equation acts as our constraint. The stars make us want to go, and the rocket equation tethers us to a limitation on our desires.

Thanks to Al, Larry, and all those others who have complimented me on the Starship Century talk about the Galaxy Garden. I am pleased but also frustrated– after 6 years since the Garden opened, it is still the only one in the world. Until somebody has the vision and means to build another with me, the best way for people to attain the unique cosmic perspective it provides is through one of my presentations. If your institution has any sort of guest lecture program, please consider having them invite me. Who knows? It might result in your own Galaxy Garden, and they are quite fun to explore!

“while I suggested the Solar System be searched for dead starships, since not everyone succeeds in their long voyages”

I am intrigued by that suggestion. It’s very practical and something we can do in the near-future. I’m interested in any goal that encourages us to put more robots into the solar system (such as a suggestion to build a telescope on the south pole of the moon), and this idea of searching for dead or dormant or broken artifacts of past alien visits (either probes or ships) interest me very much.

“Thanks to Al, Larry, and all those others who have complimented me on the Starship Century talk about the Galaxy Garden. I am pleased but also frustrated– after 6 years since the Garden opened, it is still the only one in the world. Until somebody has the vision and means to build another with me, the best way for people to attain the unique cosmic perspective it provides is through one of my presentations. If your institution has any sort of guest lecture program, please consider having them invite me. Who knows? It might result in your own Galaxy Garden, and they are quite fun to explore!”

You are welcome, Jon. As for no one yet taking up the call of making their own Galaxy Garden, it would seem that this situation is not unique for large and unique astronomical displays.

It cannot be the reason that many climates do not support plants all year round as in Hawaii, for the Sunwheel is made entirely of large stones and so far as I know no one in modern times has followed up on astronomer Judith Young’s creation:

“while I suggested the Solar System be searched for dead starships, since not everyone succeeds in their long voyages”

“I am intrigued by that suggestion. It’s very practical and something we can do in the near-future. I’m interested in any goal that encourages us to put more robots into the solar system (such as a suggestion to build a telescope on the south pole of the moon), and this idea of searching for dead or dormant or broken artifacts of past alien visits (either probes or ships) interest me very much.”

I have suggested before that we should also aim our SETI instruments at dying and dead stars. There might civilizations in those systems which could not escape the cosmic cataclysm but wanted to share their knowledge and identities with other beings as a way to preserve themselves.

At least it is a plausible reason, more than just hoping some altruistic scientists on an Earthlike exoplanet circling a Sol type star want to contact other intelligences and share information. If nothing else the beings circling a doomed sun would know they would be safe from hostile aliens, another incentive to conduct METI.

I enjoyed Jim Benford’s presentation very much. I’m a big fan of the beamrider concept, chiefly because there’s no big stupid load of fuel to lug around. The designs I’ve been exposed to all seem to use variants of high power lasers powered by solar. So why not go direct? – cut out the whole “solar power supply -> microwave transmitter” chain and go direct from sunlight itself.

The idea here is to construct a giant lens (or dual mirror) assembly as close to the sun as materials science allows, so as to intercept the maximum achievable solid angle. This promises to be far more efficient than the laser/microwave route, plus the MTBF is far better since there really is nothing to break or wear out. By perhaps using metamaterials, the lens construction can be better optimised over using conventional glass materials. We end up with a parallel beam representing all the intercepted sunlight – or perhaps a mildly converging beam with a focal point past the target. We will need station-keeping on the lens assembly to balance out momenta, and there’s also the issue of keeping orbit. Amplification is possible via multiple such systems converging their light, such that unidirectionality (albeit pulsed) can be maintained.

Is this a stupid idea because I’ve forgotten something obvious? Or is it really much better than using solar-powered lasers or microwaves?

What I don’t know is the maximum allowable W/m^2 on these newer carbon sail fabrics. Can anyone advise?

The official Web site is gone. I think the timeline is a bit much and I wonder about their idea that a written constitution would keep the generations together and behaving, but it is one of the first serious Worldship plans I recall seeing and felt it needs to at least be looked at again.

Andrew Palfreyman: There is something fundamental that you are missing. Laser and microwave sources are coherent radiation. Sunlight is not, it is incoherent. The ability to focus is fundamentally different between coherent and incoherent. Coherent radiation can be focused to a spot size that varies inversely with the size of the radiating antenna or optic. Incoherent radiation can be focused only to the angular size of the radiating source as seen at the focusing lens.

For example, the sun can be focused by an optic to the apparent diameter of the sun in our sky. But no further. Therefore a large lens close to the sun will produce a poorly focused beam because the sun will take up a large segment of the sky. That’s why there’s only so far you can go with focusing the sun for solar energy.

Jim Benford

Comments on this entry are closed.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last seven years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

On Comments

Centauri Dreams publishes selected comments on the articles under discussion here. Among the criteria for selection: Comments must be on topic, directly related to the post in question, must use appropriate language and must not be abusive to others. Civility counts. In addition, a valid email address is required for a comment to be considered. Centauri Dreams is emphatically not a soapbox for political or religious views submitted by individuals or organizations.